In the majority of telecommunication systems it is an advantage to have means for configuring the spectral characteristics of the signal, in order to be adapted to future regulations or regulations in force in different countries and to the characteristics of the channel.
The procedure forming the object of the invention is especially designed for use with signals modulated by orthogonal frequency division multiplexing (OFDM), which are known in the state of the art.
There exist antecedents in the state of the art on scalable procedures of modulation for OFDM signals like that described in U.S. Pat. No. 6,175,550 “Orthogonal frequency division multiplexing system with dynamically scalable operating parameters and method thereof”, in which an OFDM system is described which varies the time of the OFDM symbol or, equivalently, the bandwidth of the signal and the cyclic prefix in a dynamic way on the basis of measurements made by the receiver. The problem is that, in order to vary the symbol time, the sampling frequency of the signal in the converters is varied, which makes it necessary to vary the design of the analog components which are conventionally located after the digital-analog converter (DAC) of the transmitters and before the analog-digital converter (ADC) of the receivers. This is due to the fact that the spectral positions of the signal and of its responses depend on the sampling frequency, which means that the necessary filtering characteristics are different as that frequency varies. The procedure forming the object of the invention solves the problem and manages to get the variation in the duration of the OFDM symbol to be done without varying the design of the analog components, since the frequency of the converters is not varied.